The present invention relates to a piston driven, double acting rotary output pneumatic actuator. The pneumatic actuator includes a pneumatically driven reciprocating piston capable of being actuated at either end by a pressure system including a pressure source acting through a switchable 3-way valve for directing the pressure and exhaust flow to and from a desired end of the double acting piston to cause reciprocation of the piston and actuation of a rotary output member connected with the piston by a rack. A fail-safe spring mechanism is optionally provided to ensure in the event of a pressure system failure, the actuator will be set to a desired safe position.
Conventional double-acting piston driven actuators generally require a four-way valve to operate. While a four-way valve can be replaced in a small valve actuator for example by two three-way valves, i.e. the four-way valve is a functional equivalent of a pair of three-way valves, however, the four-way valve is often more than twice as complex and usually more than twice as costly as a single three-way valve.
Wherefore, it is an object of the present invention to overcome the above mentioned shortcomings and drawbacks associated with the prior art.
Another object of the present invention is to provide a simpler more economical and efficient pneumatic actuator.
A further object of the present invention is to provide a pneumatic actuator in which a three way valve controls the action of the double acting piston.
Yet another object of the present invention is to provide the double acting piston with a first end which is substantially larger than the second end thus producing a substantially greater force when the piston is actuated in one direction.
A still further object of the present invention is to provide the piston and actuator with a fail safe spring mechanism which is actuated only upon failure of the pneumatic pressure system.
The present invention provides a double-acting, piston driven actuator for providing a double action rotary powered output, comprising; an actuator housing defining a stepped bore, the stepped bore defining a larger diameter bore and a smaller diameter bore, a double acting piston reciprocally inserted within the stepped bore, the double acting piston having a larger diameter end and a smaller diameter end for matching slidable engagement within the respective larger diameter bore and a smaller diameter bore, a pressurized fluid delivery system having a first passage communicating with the larger diameter bore of the stepped bore and a second passage communicating with the smaller bore of the stepped bore, a first end of each of said first and second pressure passages communicating with a constant pressurized fluid source supplying an equal pressure thereto, a three way valve positioned in the first passage between the first end and stepped bore, the valve being controlled by a solenoid and having a first position wherein pressurized fluid supplied to the first end of the first passage is supplied to the larger diameter bore, and a second position wherein the larger diameter bore is exhausted to the atmosphere, and wherein the pressurized fluid delivery system provides the fluid from the source continuously to the smaller diameter portion of the bore.
The present invention also provides a safety mechanism having a spring biased second piston for biasing the double acting piston to a safe position upon failure of the pressurized fluid delivery system.
A three way valve is utilized in conjunction with a pneumatic pressure system to provide alternate pressure and exhaust routes from both ends of a reciprocating, double acting pneumatic piston. The substitution of the three-way valve for a four-way pilot valve also permits use of a spring driven, fail-safe accessory in which the spring, which is intended to operate the piston in the case of pneumatic failure in the system, remains compressed until needed. This operation permits the full output of the piston pinion system to be applied to the load, i.e. a pinion gear, and it also eliminates air consumption required to recompress the spring after each actuator stroke. Conventional spring return actuators utilize the spring to drive the actuator in one direction and require the pneumatically powered piston to recompress the spring as it drives the actuator in the other direction. The presently described invention, in conjunction with this fail-safe accessory spring, is, in fact, a double-acting piston driven actuator having a spring driven fail-safe override. Substitution of the three-way valve for a four-way valve in the pressure system of a small valve actuator also ensure a significant economic advantage and improved dependability.